In conventional communication systems, the DECT standard (digital enhanced cordless telecommunication), for example, a rapid call setup requires permanent synchronization of mobile components with a base station (fixed component). In this instance, what are referred to as “dummy bearers” are transmitted by the base station, or fixed component, as synchronization pulses even when no messages are being exchanged.
Every 10 milliseconds a DECT base station transmits a so-called dummy bearer as a synchronization pulse. At the proper times, here, all mobile components belonging to this base station switch to receive to synchronize themselves with the base station. The interval for a mobile component in which the receiver remains disabled may be as long as 640 milliseconds. The mobile component listens selectively here to determine whether a connection is being requested. The method is highly energy efficient for the mobile component, since in the idle mode it has to switch to receive for approx 100 microseconds only every 640 milliseconds. A drawback here, however, consists in the fact that the base station is continuously transmitting the dummy bearer as synchronization pulse every 10 milliseconds, even when no messages are being exchanged.
FIG. 1 shows a conventional communication system in accordance with the current DECT standard wherein a base station BS is connected to a communication network N. The communication network N can be, for example, a circuit-switched and/or a packet-switched communication network such as, for example, the Internet. FIG. 1 also shows two mobile components MT1, MT2 located within range of the base station BS, which can establish user channel connections via a wireless, or air, interface.
In conventional communication systems, asynchronous mobile components synchronize themselves with the synchronization pulse, or dummy bearer, of the base station, for example, when from outside the range of the DECT cell they come back within range or are reenabled. It is known empirically that this can take many tens of seconds.
The reason for this is made clear by FIG. 2, which shows the possible locations of a conventional synchronization pulse, or dummy bearer DB, at ten available carrier frequencies f as well as the time scanning of a segment, or time frame (frame FR) in 24 time slots FS. According to FIG. 2, the first twelve time slots are used for transmission by the base station BS (transmission time slots TX_BS) and the last twelve time slots FS with ascending numbering for receiving by the base station (reception time slots RX_BS). The situation is precisely the other way around for the mobile components MT. The first twelve time slots will therefore also be designated as reception time slots RX_MT, the second twelve time slots as transmission time slots TX_MT for the mobile components.
Since the mobile component MT disposes of no initial information concerning the transmitting position of the base station BS, it must also search for the receiving times RX_BS of the base station BS at the same time. Basically, each of the six connections, or occupied channels BK, as well as the much shorter dummy bearers, comes into consideration for possible synchronization. So a connection must not only be found, it must also be checked to see if the transmission originates from the requested base station BS. Information is also transmitted on the dummy bearer DB which is important to the operation of the mobile component, such as, e.g., available services, encryption, available frequencies, etc. Once it has found the base, the mobile component needs approximately another 500 ms to collect all information about the system which will be required to establish a connection.
The amount of time required here is not acceptable when, in an idle state, the asynchronous mode is the rule. Before each conversation it would now be necessary to wait for the synchronization, which in the case of the conventional devices and methods takes too long.
The standby time for a mobile component is another reason. It is initially not known to an asynchronous mobile component MT where, in the time/frequency grid according to FIG. 2, the base station BS is going to establish contact with it. To find the dummy bearer DB, the mobile component must permanently scan the entire signal space with its receiver. The power supply in the battery, however, permits only a very short time. Today's standby times of several days will therefore be excluded, since if the receiver is continuously enabled the charge in the battery will last only a few hours. In the case of conventional mobile components and/or base stations, of the Gigaset type, for example, there are currently three different power-down modes:
Green DECT Mode:
Under certain conditions, the base station BS will cut its transmitting power to a lower value. The receiver-scanning slots will also be reduced to a lower value.
The primary rationale behind the idea of going to this operating mode was to achieve an overall reduction in network power consumption by the base station. Lower power consumption in this case was in fact more of a welcome by-product, although it was not explicitly promoted. Transmission power reduction has produced its effect only if certain requirements have been met:                One and only one mobile component has been logged on to the base station.        This mobile component and this mobile component only has been placed in the charging cradle and has successfully identified itself to the base station via the charging contacts.        
This mode therefore finds application only at base stations with a charging cradle.
ECO Mode:
This is a static setting at which transmitting power is cut systemwide (base station and mobile component/mobile components). The user enables this setting by menu, and it remains valid permanently. Transmitting power will from then on never be increased, even in the case of bad connections. The ECO mode state is shown on the display.
The ECO and green DECT modes can be used independently in combination. In green DECT mode a somewhat lower transmitting power can be selected than in ECO mode.
Low Transmitting Power in Mobile Component:
Conventional mobile components, such as the GIGASET 2000C for example, have recently appeared, which on the basis of reception quality and signal strength decide whether transmitting power can be decreased. Transmitting power will then be decreased in the mobile component but not in the base station. Subsequently it can be switched back to high transmitting power during a call, the switching being handled technically during a handover. At the beginning of a connection the system will operate at high transmission power.
It is also known that the base station transmits a reduced-power dummy bearer. But this still doesn't solve the basic problem, that is, how to dispense with synchronization pulses, or dummy bearers, altogether during idle periods, e.g., at night. Current solutions work only if a single mobile component is logged onto the system and, as described above, this component remains in the charging cradle at the base station.